Without limiting the scope of the present invention, its background is described with reference to testing hydrocarbon formations, as an example.
It is well known in the subterranean well drilling and completion art to perform tests on formations intersected by a wellbore. Such tests are typically performed in order to determine geological or other physical properties of the formation and fluids contained therein. For example, parameters such as permeability, porosity, fluid resistivity, temperature, pressure and bubble point may be determined. These and other characteristics of the formation and fluid contained therein may be determined by performing tests on the formation before the well is completed.
It is of considerable economic importance for tests such as these to be performed as soon as possible after the formation has been intersected by the wellbore. Early evaluation of the potential recovery from a formation is very desirable. For example, such early evaluation enables completion operations to be planned more efficiently.
Where the early evaluation is performed during drilling operations, the drilling operation may be performed more efficiently in that the results of the early evaluation may be used to adjust the drilling parameters. For example, formation testing equipment may be interconnected with a drill string so that, as the wellbore is being drilled, formations intersected by the wellbore may be periodically tested.
It has been found, however, that conventional formation testing equipment is not suitable for interconnection with a drill string during a drilling operation. For example, typical formation testing equipment requires absolute downhole fluid pressure for operation. Typically, it is necessary to provide precharged gas chambers or other pressure reference devices to reach the required fluid pressure to appropriately actuate the equipment. Additionally, such equipment usually requires that specific steps, such as opening and closing of valves and changes of configurations, happen upon attaining specific absolute fluid pressures. Accordingly, an operator at the surface must apply such absolute fluid pressures at the surface using pumps and simultaneously observe the fluid pressure in the wellbore and drill string to determine whether such absolute fluid pressure has been reached.
Therefore, a need has arisen for an early evaluation formation testing apparatus which is not cumbersome to operate or failure prone and does not rely upon absolute fluid pressure for actuation or changes in configuration. A need has also arisen for an early evaluation formation testing apparatus that provides for valve opening and closing as well as changes in configuration upon the release of pressure or upon reaching a desired differential pressure at the equipment.